Legacy Codebase Migration Expert at Mercor

Legacy Codebase Migration Expert | $200/hr | Worldwide Remote | Part-Time Contract

Mercor is partnering with a frontier AI research lab to find experienced software engineers with deep, hands-on expertise in legacy codebase migration and modernisation. If you've personally led or made substantial contributions to complex, production-grade migrations — especially in high-reliability industries — this is a compelling opportunity to apply that expertise to cutting-edge AI research.

What You'll Do

• Design, implement, review, and evaluate complex codebase migration and modernisation tasks.
• Analyse legacy code, dependencies, APIs, databases, build systems, and infrastructure to determine safe migration strategies.
• Preserve functionality, backwards compatibility, data integrity, security, and performance throughout migrations.
• Develop tests and validation strategies to detect migration regressions and behavioural differences.
• Evaluate AI-generated migration solutions for correctness, completeness, maintainability, and production readiness.

Relevant Migration Experience

Candidates should have deep expertise in one or more of the following areas:

• Language/version upgrades: Java 8 → 17/21, legacy .NET → modern .NET, Python 2 → 3, PHP 7 → 8
• Language rewrites: COBOL → Java/Python, JavaScript → TypeScript
• Frameworks: Angular, Rails, Django, Spring/Spring Boot, ASP.NET, Next.js/Astro, and other major framework upgrades
• Databases & ORMs: Oracle/MySQL → PostgreSQL, SQL → NoSQL, Hibernate → jOOQ, Sequelize → Prisma, raw SQL → ORM
• Infrastructure: VMs/bare metal → containers, Docker/Kubernetes, cloud-native architectures
• CI/CD: Jenkins/Travis → GitHub Actions, GitLab CI, or modern deployment pipelines
• Build/package tooling: Maven → Gradle, Webpack → Vite, CRA → Next.js, npm → pnpm
• APIs: REST → GraphQL, HTTP/REST → gRPC, SOAP/legacy APIs → modern interfaces
• Authentication: Legacy auth → OAuth/OIDC, SAML/SSO, modern identity and authorisation systems
• Repositories: Polyrepo → monorepo using Bazel, Nx, Turborepo, or similar
• Testing: Migration of unit, integration, browser, and E2E testing frameworks
• Dependencies/SDKs: Replacement of deprecated or EOL libraries, APIs, runtimes, and vendor SDKs

Ideal Background

• 5+ years of professional software engineering experience, ideally at a Senior, Staff, Principal, or equivalent level.
• Personally owned or made substantial technical contributions to large-scale production migrations.
• Experience with mature systems involving technical debt, complex dependencies, legacy integrations, and significant regression risk.
• Strong knowledge of compatibility, testing, observability, staged rollouts, rollback strategies, and behavioural equivalence.
• Ability to reason deeply about unfamiliar codebases and diagnose subtle migration failures.
• Especially valuable: Engineers who have modernised core banking, payments, trading, insurance, healthcare, telecom, or other high-reliability systems.
• Also highly valued: COBOL/mainframe experience with technologies such as z/OS, CICS, JCL, DB2, VSAM, batch processing, and COBOL-to-Java/Python migrations.

Why Join

• Apply your migration expertise to help shape how frontier AI models understand and execute complex software modernisation.
• Work on technically challenging problems modelled after real-world, production-scale legacy systems.
• Contribute deep enterprise migration knowledge without needing an open-source maintainer background.
• Opportunity for ongoing, expanding work as the research program grows.